[import/no-unused-modules] not correctly handling export { default } from 'foo' syntax

[richardxia]

I've been really interested in using the import/no-unused-modules rule in one of my React projects, but it seems to be incorrectly reporting an error when it sees the export { default } from 'foo' syntax:

/usr/src/app/app/pages/About/index.js
  1:1  error  exported declaration 'default' not used within other modules  import/no-unused-modules

It's been a bit tricky for me to reproduce with a smaller example, as it seems to be somewhat reliant on the Babel and Webpack plugins, but I have been able to produce a branch of my project with 95% of the files removed and still demonstrate the issue. I think I've gotten the problem narrowed to the following four files in that branch:

//==============================================================================
// app/init.jsx
import React from 'react';
import ReactDOM from 'react-dom';
import { BrowserRouter } from 'react-router-dom';
import Routes from './routes';

ReactDOM.render((
  <BrowserRouter>
    <Routes />
  </BrowserRouter>
), document.getElementById('root'));


//==============================================================================
// app/routes.jsx
import React from 'react';
import { Route, Switch } from 'react-router-dom';

import About from './pages/About';

export default () => (
  <Switch>
    <Route path="/about" component={About} />
  </Switch>
);


//==============================================================================
// app/pages/About/index.js
export { default } from './About';


//==============================================================================
// app/pages/About/About.jsx
import React from 'react';

export default class About extends React.Component {
  render() {
    return (
      <article>
        <header>
          About the SF Service Guide
        </header>
      </article>
    );
  }
}

Any help I could get with this would be greatly appreciated. If there's a way for me to dump out extra logging information, I'd be willing to attach it here.

---

Here are the versions of relevant packages, and you can check out the package.json in the branch I linked to for the full details:

• eslint-plugin-import@2.20.0
• @babel/core@7.4.4
• webpack@4.17.4

On the branch I linked to, you should be able to reproduce the problem with the following commands:

git clone https://github.com/ShelterTechSF/askdarcel-web.git -b test-unused-modules
cd askdarcel-web
npm install
npm run lint

[ljharb]

It's possible the ExportMap needs a fix to handle export { default } from.

[richardxia]

Thanks for pointing that out. I've started adding console.log() statements to attempt to dump out some of the intermediate data, and I'm seeing the following ExportMap data for each file:

ExportMap {
  path: '/usr/src/app/askdarcel-web/app/init.jsx',
  namespace: Map {},
  reexports: Map {},
  dependencies: Set {},
  imports:
   Map {
     '/usr/src/app/askdarcel-web/node_modules/react/index.js' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] },
     '/usr/src/app/askdarcel-web/node_modules/react-dom/index.js' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] },
     '/usr/src/app/askdarcel-web/node_modules/react-router-dom/esm/react-router-dom.js' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] },
     '/usr/src/app/askdarcel-web/app/routes.jsx' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] } },
  errors: [],
  mtime: 2020-01-27T01:06:00.000Z }

ExportMap {
  path: '/usr/src/app/askdarcel-web/app/routes.jsx',
  namespace: Map { 'default' => {} },
  reexports: Map {},
  dependencies: Set {},
  imports:
   Map {
     '/usr/src/app/askdarcel-web/node_modules/react/index.js' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] },
     '/usr/src/app/askdarcel-web/node_modules/react-router-dom/esm/react-router-dom.js' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] },
     '/usr/src/app/askdarcel-web/app/pages/About/index.js' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] } },
  errors: [],
  mtime: 2020-01-27T01:06:00.000Z }

ExportMap {
  path: '/usr/src/app/askdarcel-web/app/pages/About/index.js',
  namespace: Map {},
  reexports:
   Map {
     'default' => { local: 'default', getImport: [Function: getImport] } },
  dependencies: Set {},
  imports: Map {},
  errors: [],
  mtime: 2020-01-26T19:46:48.000Z }

ExportMap {
  path: '/usr/src/app/askdarcel-web/app/pages/About/About.jsx',
  namespace: Map { 'default' => {} },
  reexports: Map {},
  dependencies: Set {},
  imports:
   Map {
     '/usr/src/app/askdarcel-web/node_modules/react/index.js' => { getter: [Function],
       source: [Object],
       importedSpecifiers: [Set] } },
  errors: [],
  mtime: 2020-01-27T01:06:00.000Z }

I'm having a little bit of difficulty trying to tell if the above output is correct, since I don't know what the precise definition of each attribute of ExportMap should be, but I do at least see each imported/exported name appear at least once.

I'm willing to attempt to submit a fix, but I think I need help determining if the bug is in the ExportMap or if the bug is in no-unused-modules.js.

[ljharb]

I'm not really sure :-) maybe start with PR with a failing test, and we can iterate on it together?

[richardxia]

Sounds good to me. I'm a bit busy the next couple of days, but I'll have some time to work on this this weekend, if not earlier.

[maniator]

@ljharb -- any updates on getting what @richardxia worked on into the next release? 😄